Adjusting devices for free piston machines



Jan. 29, R- HUBER ADJUSTING DEVICES FOR FREE PISTON MACHINES Filed Aug. 14, 1955 q 2 She ets-Sheet 1 26 42 M 29 K h r g E6- ?fa la 5 g. v y

z 0 a t //\/\/EN7'0R I Z zaierzkgp A TTOFP/VEK? Jan. 29, R. HUBER ADJUSTING DEVICES FOR FREE PISTON MACHINES 2 Sheets-Sheet 2 Filed Aug. 14, 1953 Ill 16 .4

kSWi i TKA w "MU T M mm United States Patent ADJUSTING DEVICES FOR FREE PISTON MACHINES Robert Huber, Bellevue, France, assignor to Societe dEtudes et de Participations, Eau, Gaz, Electricite, Energie, S. A., Geneva, Switzerland, a society of Switzerland Application August 14, 1953, Serial No. 374,291

Claims priority, application France April 30, 1953 2 Claims. (Cl. 60-43) The present invention relates to adjustment devices for free piston machines and its object is to provide an adjustment device which is better adapted to meet the requirements of practice than those used up to the present time.

One of the characteristics of free piston machines lies in the fact that the length of stroke of their pistons is variable within given limits. This variation of the length of stroke corresponds in particular to a variation of the outer dead center position of the pistons under the eifect of the combustion of fuel introduced in the power cylinder of the machine. On the contrary, the inner dead center of the pistons, that is to say their position at the end of their inward stroke, during which compression takes place in the power cylinder (the machine working on the two-stroke cycle) practically does not vary, at least as long as the feed pressure of said power cylinder remains unchanged or approximately so.

However the variation of position of the outer dead center must remain within certain limits. For instance, what will be hereinafter called the minimum outer dead center position, that is to say the outer dead center position corresponding to the minimum stroke of the piston or pistons, must be such that the power pistons, upon every outward stroke thereof, open the inlet ports and the exhaust ports of the power cylinder. On the contrary, the maximum outer dead center position, that is to say the outer dead center position corresponding to the maximum length of stroke of the piston or pistons, must be such that the pistons are always prevented from coming into contact with the ends of their respective cylinders.

Up to the present time, the outer dead center position was kept within said limits by means of abutments in the form of cams which imposed to the amount of fuel introduced into the power cylinder a lower and an upper limit not to be exceeded. However when such cams are used, as their action does not depend directly upon the position of the outer dead center on every stroke, safety margins must be provided so as to make provision for a possible misadjustment of the machine. This'is why the use of such cams restricted the range within which the outer dead center was truly variable- Furthermore, within the limits determined by "said cams, the length of the strokes may undergo undesired variations due also to misadjustments and not to variations of load of the machine.

The object of my invention is to obviate these drawbacks.

It consists chiefly in providing, in addition to the usual fuel feed adjustment member working in response to variations of the load of the free piston machine, correcting means for reducing, at least in the vicinity of the minimum and/or maximum outer dead center positions of the pistons, the amount of fuel determined by the usual adjustment member by an amount variable in re- 2,779,156 patented Jan. 29, 1957 sponse to variations of the length of stroke, this amount increasing. when the stroke, and therefore the outward displacement of the outer dead center, increases and vice versa.

Other features of my invention will become apparent in the course of the following detailed description of some specific embodiments thereof, with reference to the accompanying drawings, given merely by way of example, and in which:

Fig. 1 diagrammatically shows, partly. in section, a free piston auto-generator provided with adjustment means according to an embodiment of my invention;

Figs. 2 and 3 show two detail modifications of these adjustment means;

Fig. 4 is an explanatory diagram;

Fig. 5 shows an accumulator pump for the injection of fuel provided with correcting means according to my invention.

The auto-generator illustrated by way of example includes in a conventional fashion, as shown by Fig. l, a power cylinder 1 provided close to its ends with inlet ports 2 and exhaust ports 3. Two compressor cylinders 4 (only one of them being shown in Fig. 1) provided with intake valves 5 and discharge valves 6 are located on either side of the power cylinder. A casing 7 which surrounds power cylinder 3 acts as a reservoir for air intended to feed and scavenge power cylinder i, the discharge valves 6 being provided in partitions 8 which separate casing '7 from each of the compressor cylinders i.

In power cylinder 1 and cooperating therewith are provided two power pistons 9 working in opposed directions and synchronized by a synchronizing device which will be hereinafter more explicitly referred to. Each of the power pistons 9 is rigid with a compressor piston ilk which divides the corresponding cylinder 4 into two chambers 11 and 12. Chamber 11, which is on the side of power cylinder 1 and is provided with valves 5 and 6, constitutes the compressor cylinder proper, while the other chamber 12 constitutes a return energy accumulator containing a cushion of air which stores up energy during the outward movements of pistons 9, it) (during which fuel is burned in the power cylinder and fresh air is sucked in into the chamber 11 of the compressor cylinder) and gives this energy back to the moving parts of the system during their inward strokes (during which compressions take place in the power cylinder and in the chamber 11 of the compressor cylinder).

Fuel is injected into power cylinder 1, in which pistons 9 are working on a two-stroke cycle, by means of one or several injectors 13 disposed in the central transverse plane of power cylinder 1. injection of fuel takes place when the pistons are near their inner dead center position (which is that shown by Fig. 1). Fuel burns in the highly compressed air which is present at this time between opposed pistons 9. Due to this combustion. pistons 9,-10 are driven outwardly to stop in their outer dead center position when the cnergv due to this cornbustion has been absorbed by the resistant energies constituted by the energy stored up in accumulator 12, the energy necessary for sucking in fresh air into chamber 11 and the frictional energies. The outward stroke must be sufficiently long to enable pistons 9 to clear the intake ports 2 and the exhaust ports 3 of power cylinder 1, so that air can enter cylinder 1 through ports 2 and the combustion gases incompletely expanded and mixed with the excess of scavenging air can flow out through exhaust apertures 3. This mixture of gas and air under pressure is fed through a conduit 14 toward the power gas receiver, for instance a turbine T.

As above stated, the opposed movements of movable parts 9, 10 are synchronized by a synchronizing device which may be of any suitable kind. However this device is preferably in the form of a system of crossed levers 15, 16 and connecting rods 17, 18, 19 and 20, connected by hinges 21 and 22 to rods 23, 24- rigid respectively with the two moving structures 9, 10. Such a synchronizing device is fully described in my U. S. Patent No. 2,741,232.

Injector 13 is fed with fuel by means of an injection pump 25 of any suitable construction. This pump receives fuel from a conduit 26 and discharges this fuel into a conduit 27 which leads to injector 13. The pump piston. is controlled for instance by a cam 28 fixed on a rod 29 rigid with piston 9, 10 and passing in a fiuidtight fashion through the end of cylinder 4. Cam 28 is shaped and disposed in such manner that the feed of fuel by the pump and the injection through the injector take place, at least approximately, when the two piston systems are in their inner dead center positions. Adjustment of the amount of fuel delivered by the pump is obtained in the usual manner, for instance by means of rack 3t adapted to rotate the pump piston about its axis. This rack is moved in response to variations of the load of the free piston machine, for instance in response to variations of the speed of the turbine operated by the power gases supplied by the auto-generator, said speed variations being transmitted to rack 36 by a governor R driven by the turbine.

According to the main feature of my invention, the amount of fuel injected by injector 13 is controlled not only by adjustment member 3% but by a correcting device which works directly in response to variations of the position of the outer dead center of pistons 9, it). This c0rrecting device is arranged to act at least during the periods where the pistons are reaching, at the end of their outward stroke, outer dead center positions close to the minimum outer dead center position or to the maximum outer dead center position. The effect of this correcting device is to reduce the amount of fuel injected by injector 1.3 by a quantity which is the greater as the outward stroke is longer or, in other words, which is the smaller as the outward stroke is shorter. Consequently, When the pistons are close to the lower limit of their outer dead center position range, the amount of fuel that is injected increases quickly. This quick increase of the rate of feed of fuel for objectionable shortenings of the length of stroke has for its result immediately to restore the minimum length of stroke.

Similarly, when the pistons are moving with strokes approximating the admissible maximum length of stroke, any increase of this length produces a quick reduction of the amount of fuel fed into the power cylinder, which restores the length of stroke to its admissible maximum value.

Thre are many possible constructions of such a correcting device. For instance, I might provide by-pass means acting either upon the intake conduit or on the discharge conduit of the pump, these by-pass means being controlled by the correcting device.

When the combustion pump is an accumulator pump, 1 may also vary the storing capacity of its accumulator in accordance with the action of the correcting device.

According: to a particularly advantageous embodiment of my invention, I combine with the injection pump proper a second pump which, when the pistons are reaching their outer dead center position, creates in the discharge circuit of the injection pump a vacuum the importauce of which varies in accordance with the position of the outer dead center. When the injection pump is beginning its discharge stroke and the pistons are moving toward their inner dead center position, this injection pump must first make up for this vacuum (which has been created previously in its discharge circuit) before beginning the useful discharge toward injector 13. The amount of fuel which is actually injected into the power cylinder is therefore equal to the difference between the whole of the fuel discharged by the injection pump (which is adjustable by the control means of this pump) and the quantity, variable as a function of the outer dead center position, which is necessary for making up for the vacuum created by the auxiliary pump.

For instance, in the construction illustrated by Fig. l, i connect with the discharge conduit 27 of injection pump 25 a conduit 31 which is connected to the cylinder 32 of an auxiliary pump the piston of which is designated by reference numeral 33. When this piston is moving up from its lowermost position, which is that illustrated by Fig. 1, it immediately opens port 34 through which a by-pass conduit 35, branching off from conduit 31 and provided with a check valve 36, opens into cylinder 32. onsequently, during the upward movement of piston 33, the fuel discharged by said piston passes through by-pass conduit 35 into a groove 37 of piston 33, whence this fuel can escape to the outside, for instance to a tank, through a conduit 33. When piston 33, after its upward stroke, starts moving down in cylinder 32, it creates in this cylinder a vacuum the importance of which depends upon the importance of the corresponding upward stroke of said piston. it is this vacuum which has to be made up for by pump 25 before fuel is fed to injector 13.

The piston 33 of the auxiliary pump is controlled when pistons 9, it are getting close to the end of their outward stroke by a cam 39 which is also fixed to rod 29 and which may be rigid with the cam 23 which controls the piston of injection pump 25. Cain 39, which is acting upon piston 33 through a roller id, must have the shape indicated by Fig. 1, that is to say includes at its end two inclined lines 390 and 3% between which there is a horizontal portion 3%.

Portion 39b is operative when the free pistons are getting close to the minimum outer dead center position, whereas part 3% acts when the free pistons stop close to the maximum outer dead center position. Finally, portion 390 is in operation during the average strokes for which the outer dead center position is between the minimum and the maximum positions.

The correcting effect of the auxiliary pump 32, 33 is clearly shown by the diagram of Fig. 4. In this diagram, the abscissas C correspond to the lengths of stroke and the ordinates Q correspond to the amounts of fuel injected on every stroke into the power cylinder.

For a given working pressure, the length of stroke, and consequently the amount of air compressed and discharged by piston 10, and also the amount of power gases issuing from the exhaust ports 3 of power cylinder .l, are approximately proportional to the fuel feed rate into said cylinder. This feed rate depends first upon the position of the control member 30 of injection pump 25, this member being controlled by the power governor of the plant. It is supposed that, under the influence of control member 30, the fuel feed in volume supplied by injection pump 25 varies along straight line a for the lengths of stroke corresponding to outer dead center positions which range from the minimum to the maximum outer dead center positions. At the same time, the amount of vacuum produced by auxiliary pump 31, 32 controlled by a cam 39 having the shape shown by Fig. 1 varies as a function of the stroke as shown by curve I? of Fig. 4. The amount of fuel which is actually injected into the power cylinder, for every length of stroke, being equal to the difference between the volumes indicated by lines a and b, therefore varies as a function of the stroke as shown by curve c of Fig. 4. This curve shows that the amount of fuel injected quickly increases when the length of stroke has a tendency to become lower than the admissible minimum value corresponding to the minimum outer dead center position. This tendency is therefore immediately and etficiently remedied and the stroke of the free pistons keeps at least its minimum value. On the other hand, when the length of stroke has a tendency to exceed its upper limit corresponding to the maximum outer dead center position, the amount of fuel that is injected quickly decreases whereby the pistons cannot move beyond the upperlimit'of theirdead centerposition. As the correct? ing action exerted by auxiliary pump 32, 33 is immediately effective from one stroke to the next one, the safety margins which had to be provided up to the present time and which considerably reduced the possibilities of variation of stroke of the movable pistons can according to the present invention be considerably reduced or even wholly eliminated.

It is possible, by applying the main feature of the invention, to dispense with the cams forming abutments which, in the conventional free piston machines, limit the field inside which the injection pump control member can be freely displaced. However, in some cases, it will be advantageous to keep such abutments together with the arrangement which constitutes the essential feature of the invention. In this case, it is however possible considerably to increase the intervals between the minimum and maximum abutments due to the reduction or even the elimination of the safety margins.

When the cam which controls the auxiliary pump has the form indicated by Fig. 1 (the operation of the pump is then that indicated by the curve b of Fig. 4), this pump has a correcting effect only when the piston strokes are close to the limits inside which these strokes must be maintained. However the correcting action of the pump can be extended to the whole range of possible stroke lengths by giving. the cam which controls this auxiliary pump a suitable shape, for instance one of those indicated by Figs. 2 and 3.

In the case of Fig. 2, cam 41 which controls the piston of the auxiliary pump has a uniform slope over its whole length. Consequently, the auxiliary pump has a uniform correcting effect whatever be the value of the momentary stroke which corresponds to the load of the system. As soon as the stroke of the free pistons 9, has a tendency to vary from the value corresponding to the momentaneous load of the system, the auxiliary pump comes into play to reestablish the normal value of the length of stroke by producing, for too long a stroke, a reduction of the amount of fuel to be injected and, for too shorta stroke, an increase of the feed of fuel to be injected.

The cam 42 of Fig. 3 is a modification of the cam illustrated by Fig. 2.

In the construction of Fig. 3, cam 42 includes three different portions 42a, 42b, 42c. Portions 42a and 425, which are brought into play when the length of stroke is close to the maximum and minimum values thereof, have a steeper slope than portion 420 which is located between portions 42a and 42b and which operates for intermediate lengths of stroke. In the vicinity of the minimum and maximum limits of the length of stroke, the correcting action of the pump is therefore more intensive than inside the range for which the lengths of strokes are variable.

From what precedes, it is apparent that it is possible to obtain the desired correcting effects by a suitable choice of the shape of the cam which operates the auxiliary pump, which shape must of course take into account the law according to which the injection pump control member varies the amount of fuel delivered by this pump.

Fig. 5 shows, on an enlarged scale, a combination of injection pump and correcting pump, made according to a particular embodiment of the invention, which seems to be particularly advantageous and in which the injection pump is a pump including two accumulators. One of these accumulators feeds one or several direct injection nozzles mounted on the power cylinder 1, whereas the other accumulator supplies one or several prechamber injection nozzles also opening into said power cylinder. The injection pump of said system therefore corresponds to the pump described in the copending application filed by Helge Horgen for Improvements in Fuel Injection Devices for Diesel and Similar Engines, Ser. No. 369,054, filed July 20, 1953, now abandoned.

In Fig.5, the piston of the injection pump is designated by 43. This piston may be rotated about its axis; by means of control member 36 and includes in a conventional manner an oblique face 44 which, according to the angular position of piston 43 about its axis, opens at a variable time, during the piston upward stroke, the orilice 45 through which the suction conduit 46 opens into the cylinder 47 in which piston 43 is working. The discharge of liquid by piston 43 stops when orifice 45. starts being cleared by face 44 of the piston.

As long, as orifice 45 is closed, piston 43 drives the. fuel present in cylinder 47 above said piston, first past a check valve 48 into an accummulator 49 which serves to feed fuel to the prechamber injectors. Piston 50, which is movable in the chamber of accumulator 49, is subjected to the thrust of a second piston 51, itself subjected to the air pressure existing in a space 52 and also to the action of a spring 53. The upward movement of pistons 50 and 51 under the effect of the fuel discharged into accumulator 49 by piston 43 is limited by an abutment 54. The amount of fuel which is stored up in accumulator 49 is consequently constant so that the amount of fuel injected by the prechamber injection nozzles. is also constant.

After accumulator 49 has been filled with the amountof fuel determined by the position of abutment 54, piston 43 discharges the remainder of this fuel past a valve 55 into a second accumulator 56 which serves to feed the direct injection nozzle means through a conduit 27a. In this second accumulator 56, there is provided a piston 57 submitted to the thrust of a second piston 53 movable in chamber 52 and which undergoes the action of the air under pressure present in this chamber and also the action of a spring 59. The respective dimensions of pistons 50 and 51 and also those of pistons 57 and 58 and the strengths of springs 53 and 59 are chosen in such manner that the pressure to which the piston 50' of accumulator 49 is subjected is slightly lower than thepressure to which the piston 57 of accumulator 56 is subjected. Thus the two accumulators are filled in the manner which will be hereinafter described.

When piston 43 reaches its uppermost position in cylinder 47, it lifts a hollow valve 60 which forms the valve seat of the above mentioned valve 55 and which, in normal position, closes by its head 61 accumulator 56 with respect to conduit 27a. However, when piston 43 lifts sleeve valve 60, the communication is opened between accumulator 56 and conduit 27a and the'fuel contents of this accumulator are injected by the direct injection nozzle means.

The injection of fuel by the prcchamber injection nozzle means, which takes place immediately after that effected by the direct injection nozzle means, is controlled by a valve 62 movable in a cylinder 63 and provided with a groove '64 located below its head 65'. In the wall of cylinder 63 open, at different levels, two conduits, one, 66, provided with a check valve 67 and connected through conduit 68 with accumulator 49, whereas the other, to Wit 69, is connected to the prechamber injection nozzle means. The supply to the prechamber injection nozzle means of fuel from accumulator 49 takes place when valve 62 is in its upper position for which its groove 64 connects conduit 66 with conduit 69.

Of course, the discharge stroke of piston 43 and the upward displacement of valve 62 through which this valve is brought into the position for which the prechamber in jection nozzle means are fed with fuel take place on every stroke at a time when the pistons of the machine are close to their inner dead center position. These strokes are obtained, in the construction of Fig. 4, by means of a cam 70 which acts upon two levers 71 and 72, the first of which produces upward movement of piston 43, whereas the second one produces upward movement of valve 62. Downward movement of these parts 43 and 62 is ensured by a spring 73 and 74 respectively. Cam 70 oscillates about the axis of its shaft 75, this axis being advantageously connected to the axis of the oscillating lever of the synchronizing means, in view of the fact that it is this lever 15 which has important angular movements when the pistons are close to their inner dead center position.

Concerning the correcting auxiliary pump, it is constituted by a piston 76 which is movable in a cylinder 77 and which is actuated by a lever 73 controlled by a cam 79. This cam, which oscillates about the axis of its shaft 80, may have a shape analogous to that of one of the earns 39, 41 and 42 shown respectively by Figs. 1, 2 and 3. Pump 76, 77 is operated when the pistons are close to their outer dead center position. It is why the shaft 80 of cam 79 is advantageously driven by the axis of the lever 16 of the synchronizing device, as this lever has important angular displacements when the pistons of the free piston machine are close to their outer dead center position.

It follows that when piston 76 is operated by cam 79, piston 43 and valve 62 are in their lowermost position. It should be noted here that in this position valve 62 uncovers, by the top face of its head 65 (see the transverse dotted lines indicating the level of this surface for the lowermost position of the distributing valve), the oritive through which conduit 66 opens into cylinder 63.

Cylinder 63 communicates with said conduits 68 and 66. When piston 76 is moving upwardly, it drives the liquid contained in cylinder 77 past check valve 67 and through conduit 66 into the portion of cylinder 63 located above the top face of piston 62, 65, which portion communicates constantly through a conduit 81 with the feed conduit 46 of the injection pump. The liquid discharged by piston 76 can therefore escape freely through this conduit 46. When piston 76 subsequently moves down, it creates a vacuum in cylinder 77 and the importance of this vacuum depends upon the length of stroke of the movable pistons of the machine. Pump 43, 47, when it next operates, must first make up for this vacuum before it can start filling accumulator 49.

Of course, the invention is not limited exclusively to free piston auto-generators, but it might apply to free piston motor compressors.

It should also be noted that the expression free piston machines applies not only to machines in which both the inner dead center positions and the outer dead center positions may undergo variations, but also to the machines in which only one of the dead reenter positions, to wit either the outer one or the inner one is variable.

In a general manner, while I have, in the above description, disclosed what I deem to be practical and efficient embodiments of my invention, it should be well understood that I do not Wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as comprehended within the scope of the accompanying claims.

What I claim is:

1. In a machine including a power cylinder, a power piston slidable in said cylinder, a compressor cylinder, a compressor piston slidable in said last mentioned cylinder, these two pistons being rigid with each other and being freely slidable in their respective cylinders under the eifect of the forces acting thereon, the combination of a fuel feed pump, a discharge circuit for said pump leading to said power cylinder, means responsive to the load of said machine for adjusting the rate of feed of said pump in accordance with variations of said load, an adjustable auxiliary pump connected with said pump discharge circuit for withdrawing therefrom an amount of fuel proportional to the length of stroke of said auxiliary pump, and means operatively connected with said compressor piston for operating said auxiliary pump with a length of stroke the greater as the outer dead center position of said compres sor piston is farther beyond a given dead center position.

2. In a machine including a power cylinder, 2. power piston slidable in said cylinder, a compressor cylinder, a compressor piston slidable in said last mentioned cylinder, these two pistons being rigid with each other and being freely slidable in their respective cylinders under the effect of the forces acting thereon, the combination of a fuel feed pump, a discharge circuit for said pump leading to said power cylinder, means responsive to the load of said machine for adjusting the rate of feed of said pump in accordance with variations of said load, an adjustable auxiliary pump connected with said pump discharge circuit for withdrawing therefrom an amount of fuel proportional to the length of stroke of said auxiliary pump, a rod rigid with said pistons, a cam carried by said rod and follower means interposed between said cam and the piston of said auxiliary pump to operate said auxiliary pump, said cam being shaped to give the length of stroke of said piston a value the greater as the outer dead center position of said compressor piston is farther beyond a given dead center position.

References Cited in the file of this patent UNITED STATES PATENTS 2,182,063 Steiner Dec. 5, 1939 2,344,058 Pescara Mar. 14, 1944 2,425,850 Welsh Aug. 19, 1947 2,497,091 Morain et a1. Feb. 14, 1950 2,520,294 Welsh Aug. 29, 1950 FOREIGN PATENTS 794,632 France Feb. 12, 1936 

